Monitoring dust deposition

ABSTRACT

A method for monitoring a contaminated, dirty or inflammable condition within an electrical consumer appliance, comprises using a measurement device to measure a parameter that indicates an amount of dust on a surface located within the electrical consumer appliance, and using an indicator to indicate when the amount of dust on the surface exceeds an acceptable limit.

BACKGROUND OF THE INVENTION

The present invention relates to monitoring a contaminated, dirty orinflammable condition caused by fallout dust. More specifically, theinvention is directed to a new use of dust detection equipment toprovide a warning for presence or an amount of dust or fine particles ona surface in an appliance.

A main purpose of an indicator for fallout dust is prevention of fireand explosions. However, one may envisage several important purposes,e.g. (a) being able to prevent particular odor related to dust/particleaccumulations, (b) being able to improve efficiency of cooling units bypreventing large accumulations of dust on cooling ribs, since suchaccumulations impair heat exchange capability, (c) generalimprovement/increasing efficiency of cleaning/service/maintenanceprograms, i.e. demonstrating more easily a need for cleaning, or (d)being able to maintain important parameters for electrical/electronicapparatuses within given tolerances.

In general it is previously known to measure dust and particleaccumulations; however such measurements are typically made inindustrial or research related environments. U.S. Pat. No. 4,793,710discloses a method for measuring dust layers in coal mines, based uponan optical technique, and U.S. Pat. No. 5,412,221 also relates to anoptical measuring method for small particle deposition (“fallout”) inconnection with space research. U.S. Pat. No. 5,229,602 discloses anoptical method for detecting contamination layers particularly ontransparent surfaces (headlight glass, windshield) on vehicles.

SUMMARY OF THE INVENTION

However, the present invention is based on a need for safeguarding life,health and property also in a normal consumer environment, and thenbased upon solutions that can be mass produced at a low cost, especiallyin such a manner that measurement and display equipment can beintegrated in an appliance that is usual in such a normal consumerenvironment.

In a consumer market that comprises products of TV sets, audio and videoappliances, larger domestic appliances like refrigerators, stoves, etc.,small domestic appliances like coffee makers etc., personal careappliances, computer products like PC's and additional equipment forsuch products, electrical installations in dwelling units like fuseboxes/panels, electric radiators, lamps etc., it is clear that a dustmonitor may be of large interest. A dust monitor may also be used inconnection with allergy problems from which many people suffer. A goodindication of dust accumulation in a close environment of an allergicsubject may provide a good basis for demonstrating efficiency ofpossible counter measures, or provide a basis for starting such countermeasures.

As regards ordinary cleaning, a dust monitor in accordance with theinvention can of course also be an aid quite simply in demonstrating aneed for ordinary cleaning.

When the word “dust” is used in the present description of theinvention, one has in mind dust of different types, fine particles, dirtetc. A starting point is that the dust in question is fallout dirtconsisting of particles that may hover some time in the air.Additionally, within the concept of dust, it is possible to distinguishbetween house dust, industrial dust and traffic dust. House dust is amixture of fabric fibers (various forms of fabrics like cotton), andpollen (different forms of pollen, i.e. grain, grass, flower pollenetc.). Industrial dust is various types of waste products like grindingdust from wood and metals, and other waste products (contamination,pollution). Traffic dust is a mixture of asphalt, exhaust and differenttypes of gases (pollution).

Hence, the purpose of the invention is to provide a warning/indicationregarding accumulation of dust in important positions for consumers, andin accordance with the invention this has been achieved through a use ofthe type defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention shall be illuminated further by examiningcertain exemplary embodiments, and in this connection it is referred tothe appended drawings, where

FIGS. 1 a and 1 b show schematically a dust meter of an optical type, inviews from above and from a side, respectively,

FIG. 2 shows a circuit diagram for an optical detector used in the dustmeter shown in FIGS. 1 a and 1 b,

FIGS. 3 a and 3 b show a dust meter of a thermal type, in views fromabove and from a side, respectively,

FIG. 4 shows a circuit diagram for a detector in connection with thethermal dust meter shown in FIGS. 3 a and 3 b, and

FIG. 5 shows a dust meter that can be used in accordance with theinvention, in its most general form.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A concrete use of the invention is, as mentioned above, in connectionwith detecting and giving a warning regarding dust accumulation in a TVset. The embodiments now to be discussed with reference to the drawingare envisaged in such a connection, but it is emphasized once more thatalso other consumer appliances are of interest, as explained previously.In FIGS. 1 a and 1 b appear a schematic layout for a dust meter that ismountable inside a TV set. A plate 2, preferably arranged horizontallywill little by little accumulate dust and particles that are depositedfrom an air space above the plate. A light source 1 is arranged at theleft end of the plate 2, which light source emits light in such a mannerthat it propagates at least along a top side of the plate 2, and inaddition in a space above the plate that supposedly does not contain anydust, i.e. at such a height above the plate that it is improbable that adust layer will ever grow that high. The two main light paths appear inFIG. 1 b, i.e. two light paths indicated by two divergent pairs ofbroken lines. (Light may of course also spread outside of thesedirections, but such light will not be of any use in connection with anactual measurement.)

A screen 3 provides a division between two light beams of interest, thetwo light beams being termed A and B, i.e. A in the dust layer area, andB in the air space above the dust layer.

As appears from FIG. 1 a, it is favorable to have a wide light beam, ormake the light beam spread such as shown in FIGS. 1 a and 1 b, along thedust layer, in order to increase measurement sensitivity and to decreaseuncertainty. A lens 4 collects both beams A and B to respectivedetection areas, where two separate detectors 6, 7 measure lightintensities. The lens 4 maybe a normal convex lens, or, such asindicated in the figures, a cylinder lens, since it may be sufficient tofocus the light in a horizontal plane. It will be favorable to buildboth detectors 6,7, the lens 4 and the screen 3 together inside a closedbox 5, indicated in the figures by broken lines.

The intensity of light beam A will be reduced when the dust thickness onplate 2 grows, while the reference light in beam B will not beinfluenced by this layer of dust. Dust on the light source 1 willattenuate both beams equally. It is possible to adjust recordable dustthickness mechanically by adapting a height of a light slit betweenscreen 3 and plate 2. The top surface of plate 2 should be dull so as toavoid reflections. As mentioned, it is favorable with a light beamhaving a certain width in a horizontal plane, and this can be achievedby virtue of a lens (not shown) between the light source 1 and plate 2,or by making the light source emit a relatively wide beam such as shownin FIG. 1 a.

Regarding an electric/electronic aspect of this matter, referred to isFIG. 2 which shows an easily realized design of electrical circuitrythat is necessary in connection with the configuration of FIGS. 1 a and1 b. The light source 1 is shown in a simple circuit at the left in thefigure, in the form of a light-emitting diode (LED), and in a detectioncircuit to the right in the figure, detectors 6 and 7 are shown asphototransistors connected in a simple manner to provide input signalsfor a differential amplifier 8 (it is also possible to use photodiodes.)As the dust thickness increases, and thereby beam A is attenuated, aratio between two voltage inputs to the differential amplifier 8 isupset, and voltage output form the differential amplifier 8 willincrease. This is detected by virtue of comparator 9 which compares to afixed reference voltage delivered by a simple voltage divider. If outputfrom comparator 9 exceeds a certain voltage, an alarm light diode 10 isswitched on, and this represents a possible indication that an undesiredthickness of the dust layer has been reached.

The electronic circuitry after the photo detectors 6,7 will in realitydepend on how possible dust recordal shall be indicated, i.e. if, suchas shown here, a light diode shall be lit, if a measurement value shallbe exhibited in a display or possibly in a TV screen, or a specialindication may also be cutting supply voltage from the TV set.

Hence, in the shown embodiment, an exceeded dust limit is marked bylighting a light diode, and by outputting a logic “high” signal.However, it is quite feasible to grade the alarm for indicating severalthicknesses of dust, but this will then require a somewhat differentcircuit solution than what has been shown.

If the detector is to be located in an area where light can get in, thelight source 1 should be modulated so that a receiver part can be ACcoupled; however, such a solution has not been shown in the drawings.The solution with a modulated light source will of course be a littlemore costly.

As a matter of principle, it will of course also be possible to transmitlight “transversely” to the dust layer; that is in FIG. 1 b with a lightsource situated above plate 2, preferably with a light beam expandingelement in the form of a lens, with a transparent or reflecting plate 2,and with detection below or above the plate, respectively. A referencemeasurement must then be made in some other manner, e.g. with a detectorattached to the light source in a dust-free configuration, i.e built-intogether with the light source.

Experiments that have been conducted in accordance with the solutionshown in FIGS. 1 a, 1 b and FIG. 2, show that light traveling along adust surface, will be attenuated approximately in proportion to dustthickness. Experiments further indicate that density of the dust layeris of little importance with this detection solution.

Quite different measurement techniques than optical detection can alsobe used regarding detecting dust layers, and in FIGS. 3 a and 3 b isshown a thermal detector for the same purpose. The principle utilizedhere, is based on the fact that a dust layer will have an insulatingeffect, so that temperature of a heated surface will increase withincreasing dust thickness. To achieve a reliable detection, a referencemeasurement toward a point that does not depend on the dust layer,should be used.

The thermal detector is built on an insulating support D in order tomaintain a heat loss that is as small as possible in that direction.Heating elements may be two resistors 11 and 12 connected in paralleland placed on respective cooling surfaces 15 and 16, as shown in FIG. 3a which is a top view of the detector. The cooling surface 15 is anactual dust sensor, which little by little shall be coated by dust,while cooling surface 16 is a reference. Cooling surface 16 is madeinsensitive to dust by covering it with an insulation layer E that isnot too thick. Here it is a goal that thermal resistance throughinsulation layer E shall be significantly higher than thermal resistancein a dust layer, so that such a dust layer does not influence the heatemission from the cooling surface. In order to obtain sufficient coolingdespite this, cooling surface 16 is made relatively large.

Thermistors are preferably used as temperature sensors 13 and 14. (Othertypes of sensors are of course also of interest, e.g. thermocouples.)The dust sensor, i.e. the cooling surface 15, will have a reducedcooling effect when it is gradually covered by a dust layer, so thattemperature in the thermal sensor 13 will be a function of dustthickness. Temperature in thermal sensor 14 will on the other hand staysubstantially constant, even if dust falls upon the insulation layer E.

Closely adjacent to the thermal sensors 13 and 14, the temperatureshould be substantially higher than ambient temperature. This isachieved by supplying sufficient power (about 1-5 watts), and byinsulating above the thermal sensors and the heating elements viainsulation layer C. Physical dimensions of insulating layer C may beabout 5×5 cm with a maximum height about 2 cm, as seen in FIG. 3 b.

An example of a circuit diagram in connection with the thermal detectorshown schematically in FIGS. 3 a and 3 b, appears in FIG. 4. In theexample shown in FIG. 4, an end part of a detection circuit is rathersimilar to that shown in FIG. 2 regarding the optical detection circuit,i.e. from a differential amplifier 17 through a comparator 18 and to analarm light-emitting diode 19. However, the photo-transistors 6 and 7 inFIG. 2 are exchanged for thermistors 13 and 14 in FIG. 4, for deliveringsignal voltages to the differential amplifier 17. Each one of thethermistors 13 and 14 is part of a voltage divider together withresistors R2 and R1, respectively. Heating elements 11 and 12 are partof a separate, simple parallel circuit.

All resistors in the above-described, including the heating elements,should have a tolerance of 1% or better, while accuracy of supplyvoltage U is not critical.

Both described solutions for detecting dust layer thickness are simple,and the total cost in mass production can be expected to be less thanNOK 10 in both alternatives, with the thermal solution being the lessexpensive one.

One further possibility for detecting a dust layer is a mechanicalsensing method, which method can be based upon a strain principle or apressure principle. The strain principle is based on bending a plate dueto dust weight. In such a case a strain gauge may be an actual sensor.When the pressure principle is used, a pressure sensor on an undersideof an accumulation surface senses weight of the dust layer; that issuperpressure growing gradually in addition to start pressure caused byweight of the surface/plate itself.

Independent of the type of sensor that is used, a signal from the sensorwill normally have to be amplified, i.e. an amplifier succeeding thesensor shall record current or voltage from the sensor, and adapt alevel for a display unit that may be of various types. In order to makerelative measurements, the amplifier should be a differential amplifierwith the sensor in a measurement bridge.

Regarding the display unit, this unit may be of several different types.As shown in FIG. 2 and FIG. 4, display takes place by virtue of a simplelight-emitting diode, which is lit when the dust layer reaches a certainthickness. It is of course also possible with a display of a moreadvanced type, e.g. for displaying an actual thickness of the dust layeras measured by a suitable unit of measurement. A seven-segment typedisplay or an intelligent display may then be utilized. Furtherpossibilities are that the display unit may control a current switch forswitching off an appliance in question if the dust thickness exceeds acritical value. Further possibilities include connection to a monitorscreen with an opportunity for text in the screen. This last mentionedsolution may be of interest if the dust monitor is to be built-in, in anintegrated manner in a TV set or a computer monitor.

In this last mentioned case it is favorable to manufacture a dustwarning unit as an individual unit, or possibly as an integral part ofan appliance. If the dust warning unit is produced as an individualunit, it must be suitable for fitting into the appliance at a latertime. As an integral part, it will be included as a production elementin an appliance, e.g. a TV set, and as previously mentioned, possibly ata very low cost.

Voltage supply may be standardized at 5.0 volts. This voltage may varywithin a given range, without influencing reliability of the dustmonitor.

As previously mentioned, it is favorable to base the dust sensor onrelative measurements, so that external and spurious influences shallnot be disturbing.

Quite generally it is important to underline that the “warning” thatshall take place, may take place in different manners. As mentionedabove, one may most easily visualize a light indicator in some form (onefurther such indicator may be a simple luminous indication with a colordependent on dust amount), but it may also be of interest to use anacoustic signal, i.e. some form of sound emission. Also, a textindication as mentioned above in connection with a TV set/computermonitor is an important possibility. Of course, one may also visualize acombination of these indication modes.

It is also favorable in certain applications to provide the possibilitythat the display may provide information that the system is operational,and that it is working.

In FIG. 5 is shown a dust measurement device in its most general form asmentioned above, i.e. independent of a physical measurement principlethat may be optical, thermal, weight-based, ultrasound-based, possiblybased on measurement of electrical characteristics like resistance,capacity etc. Absorption/attenuation of types of radiation other thanoptical and ultrasound radiation can be envisaged, e.g nuclear radiationwith a radiation source similar to the one that is utilized in smokedetectors. Thus, in this figure “the dust sensor”, which normally willrequire a voltage supply, comprises some sensor type that is able todeliver a signal depending on a dust amount that is measured. The signalpasses to an amplifier that delivers an output signal further to adisplay unit and possibly to an alarm unit. The display unit maypreferably comprise or be attached to a monitor screen, and it maypossibly be switchable on and off by virtue of a switch.

1. A method for monitoring a contaminated, dirty or inflammablecondition within an electrical consumer appliance, comprising: using anoptical measurement device to measure attenuation of a light beamtransmitted through dust that is on a surface located within theelectrical consumer appliance; and using an indicator, connected to saidoptical measurement device, to specify a measurement value that is afunction of the measured attenuation of said light beam so as toindicate a thickness of the dust on said surface and thereby indicatewhen an amount of dust on said surface exceeds an acceptable limit. 2.The method according to claim 1, wherein using optical measurementdevice to measure attenuation of light beam transmitted through the dustthat is on said surface located within said electrical consumerappliance comprises using said optical measurement device to measureattenuation of a light beam transmitted through the dust that is on saidsurface located within a television set.
 3. The method according toclaim 1, wherein using the optical measurement device to measureattenuation of beam transmitted through the dust that is on said surfacelocated within said electrical consumer appliance comprises comparing anoutput intensity of said light beam with an intensity of a referencelight beam that is not transmitted through the dust that is on saidsurface.
 4. The method according to claim 1, wherein using the opticalmeasurement device to measure attenuation of the light beam transmittedthrough the dust that is on said surface located within said electricalconsumer appliance comprises using the optical measurement device tomeasure attenuation of a divergent or expanded light beam transmittedalong and through the dust and then focused towards a photodetector viaa lens that is positioned beyond said surface.
 5. The method accordingto claim 1, wherein using the optical measurement device to measureattenuation of the light beam transmitted through the dust that is onsaid surface located within said electrical consumer appliance comprisesusing the optical measurement device to measure attenuation of a lightbeam transmitted transversely through the dust and reflected from saidsurface.
 6. The method according to claim 1, wherein using the opticalmeasurement device to measure attenuation of the light beam transmittedthrough dust that is on a surface located within an electrical consumerappliance comprises using the optical measurement device, located withinsaid electrical consumer appliance, to measure attenuation of the lightbeam transmitted through the dust that is on said surface located withinsaid electrical consumer appliance.
 7. The method according to claim 6,wherein using the optical measurement device to measure attenuation ofthe light beam transmitted through the dust that is on said surfacelocated within said electrical consumer appliance comprises using saidoptical measurement device to measure attenuation of the light beamtransmitted through the dust that is on said surface located within atelevision set.
 8. The method according to claim 6, wherein using theoptical measurement device to measure attenuation of a light beamtransmitted through the dust that is on said surface located within saidelectrical consumer appliance comprises comparing an output intensity ofsaid light beam with an intensity of a reference light beam that is nottransmitted through the dust that is on said surface.
 9. The methodaccording to claim 6, wherein using the optical measurement device tomeasure attenuation of the light beam transmitted through the dust thatis on said surface located within said electrical consumer appliancecomprises using the optical measurement device to measure attenuation ofa divergent or expanded light beam transmitted along and through thedust and then focused towards a photodetector via a lens that ispositioned beyond said surface.
 10. The method according to claim 6,wherein using the optical measurement device to measure attenuation ofthe light beam transmitted through the dust that is on said surfacelocated within said electrical consumer appliance comprises using theoptical measurement device to measure attenuation of a light beamtransmitted transversely through the dust and reflected from saidsurface.